Can my chlorine be high while SWCG output is low??

[waterbear]

Hi, all --

Just converted to a SWCG pool this summer when we replaced our vinyl liner. I've been working on the water balance to try to allow the generator to cycle on as little as possible and still maintain healthy sanitizer levels, to prevent ph rise. I've been trying to follow Waterbear's "Fine Tuning a Salt Water Pool" suggestions and have been getting some success (TA down to 120 from 150). Before I go any further, here were my levels yesterday, as tested with my brand spanking new Taylor K2006 test kit:

FC: around 11 ppm
CYA: around 75 ppm
PH: around 7.7
Hardness: around 300
TA: 120
Salt according to CompuPool CPSC36: 3200 (tends to fluctuate, though, between 3100 and 3900 -- Aquachek strips more consistently show around 3700)
25,000 gallon inground pool with attached "waterfall" spa

I thought that 11 ppm for FC seemed a little high, even with my CYA levels at 75, and that was with the generator running at 30%. So I lowered it to 20%, and will test FC today to see what happens. Is this okay -- to be running the output so low, even 30%, and having FC so high?
IF the FC is high you lower the output and/or the pump run time. You are on the right track! It will take a bit of time for the pool to stabilize so don't rush this process. I run my Aqualogic at about 8% to 15%, depending on the ambient temperature, with an 8 hour pump run time to maintain my FC at 5 ppm. My pool is open "year round".

It should also be noted that before I got my K2006 kit, I was using Leslie's (made by Taylor) DPD reagent kit, and would get a high FC color match (over the max), but within about 30 seconds the pink color would fade to more like 2-3 ppm. Does this mean anything?
YES! It means your FC is above 10 ppm! DPD will bleach out at high FC levels and when you see a "flash" of pink that fades or disappears you are seeing this bleachout effect and it means your FC is hgh. When using a DPD test you would now need to start diluting your sample with distilled water and then multiplying your test results by the dilution factor to get anything meaningful. Sounds like you have been runnning a high FC for a while and did not realize it. You can turn off the SWCG until the FC drops to the proper level and then turn it on and fine tune it. Don't be surprised if the FC does not drop for several days. You might not have a big chlorine demand at the moment.

As a side note which may offer useful info to you experts in getting a total picture of my pool, I had been working on lowering the TA to closer to 80 using Waterbear's suggestions, adding dry acid a little at a time and running the spa jets once I brought the PH down to the 7.2 range. However, I have not been able to do this constantly since we can only run the spa jets when the whole pool is on (otherwise the water level in the spa drops to below the jets), and since I leave for work in the morning before the timer turns on the filter pump, I have not aerated the pool nor added any dry acid for about a week. Would running the filter and spa jets 24/7 (and thus the SWCG) be okay when trying to lower TA, and if so, how many days do you think it would take? I'd hate to inflate my electric bill too much.

Thanks --
Jody

If your water level drops when running the spa jets then start looking for a leak or possibly a back check valve in the spa return line.
Adding dry acid "a little at a time" is not going to do the job. You need to drop the pH to 7.0, test TA, then aerate to bring it above 7.4 and repeat this until the TA is on target. You do not need to aerate but it will take longer for the carbon dioxide to gas off. There are other ways to aerate besides using your spa jets BUT if your water level drops when running the spa jets then start looking for a leak or possibly a back check valve in the spa return line.